1. Field of the Disclosure
Embodiments disclosed herein relate generally to apparatus and methods involved in cutting tools for oilfield applications. More particularly, embodiments disclosed herein relate to apparatus and methods for wear indicators on an expandable underreamer.
2. Background Art
In the drilling of oil and gas wells, typically concentric casing strings are installed and cemented in the borehole as drilling progresses to increasing depths. Each new casing string is supported within the previously installed casing string, thereby limiting the annular area available for the cementing operation. Further, as successively smaller diameter casing strings are suspended, the flow area for the production of oil and gas is reduced. Therefore, to increase the annular space for the cementing operation, and to increase the production flow area, it is often desirable to enlarge the borehole below the terminal end of the previously cased borehole. By enlarging the borehole, a larger annular area is provided for subsequently installing and cementing a larger casing string than would have been possible otherwise. Accordingly, by enlarging the borehole below the previously cased borehole, the bottom of the formation can be reached with comparatively larger diameter casing, thereby providing more flow area for the production of oil and gas.
Various methods have been devised for passing a drilling assembly through a cased borehole, or in conjunction with expandable casing to enlarging the borehole. One such method involves the use of an underreamer, which has basically two operative states —a closed or collapsed state, where the diameter of the tool is sufficiently small to allow the tool to pass through the existing cased borehole, and an open or partly expanded state, where one or more arms with cutters on the ends thereof extend from the body of the tool. In this latter position, the underreamer enlarges the borehole diameter as the tool is rotated and lowered in the borehole.
A “drilling type” underreamer is one that is typically used in conjunction with a conventional “pilot” drill bit positioned below (i.e. downstream of) the underreamer. Typically, the pilot bit drills the borehole to a reduced gauge, while the underreamer, positioned behind the pilot bit, simultaneously enlarges the pilot borehole to full gauge. Furthermore, it is conventional to employ a tool known as a “stabilizer” in drilling operations. In standard boreholes, traditional stabilizers are located in the drilling assembly behind the drill bit to control and maintain the trajectory of the drill bit as drilling progresses.
In a conventional rotary drilling assembly, a drill bit may be mounted onto a lower stabilizer, which may be disposed approximately 5 or more feet above the bit. Typically the lower stabilizer is a fixed blade stabilizer and includes a plurality of concentric blades extending radially outwardly and azimuthally spaced around the circumference of the stabilizer housing. The outer edges of the blades are adapted to contact the wall of the existing cased borehole, thereby defining the maximum stabilizer diameter that will pass through the casing. A plurality of drill collars extends between the lower and other stabilizers in the drilling assembly. An upper stabilizer is typically positioned in the drill string approximately 30-60 feet above the lower stabilizer.
A typical drilling apparatus 10 is shown in FIGS. 1A and 1B. Drilling apparatus includes a drill bit 20 disposed on the distal end of a drillstring 15, an expandable lower stabilizer/underreamer assembly 30, a drill collar 40, and an upper stabilizer 50. FIG. 1B shows expandable underreamer 30 which includes cutting elements 32 and a stabilizer pad 34. Expandable underreamer 30 is configured to travel along grooves 36 during expansion or retraction of the arms.
During underreaming operations, the cutting elements of the underreamer may wear down from the continued contact with the formation to a point at which they are no longer effective. In this condition, the cutting elements do not properly remove material from the formation, and thus affecting the gauge diameter of the bore by reducing the diameter at which it is being underreamed. This may lead to further problems when the casing is run into the bore and the gauge diameter is too small. Accordingly, there exists a need for an apparatus and/or a method to indicate to an operator when the cutting elements are no longer effectively underreaming the bore to the proper gauge diameter.